In presynaptic nerve terminals calcium and calmodulin (CaM)-dependent phosphorylation mediates the activation of tryptophan hydroxylase and tyrosine hydroxylase. CaM-induced phosphorylation of microtubule associated protein regulates neurotransmitter release. In post-synaptic cells with dopamine receptors CaM regulates adenylate cyclase, phosphodiesterase and the action of cyclic AMP. The adaptive changes of the dopamine receptor in either sub- or supersensitive state appears to be dependent on CaM translocation from membrane to cytosol compartment.